The latest results from Monday's Kenyan elections show Uhuru Kenyatta maintaining his lead in the race for president.

With more than 40 percent of polling stations reporting, Kenyatta leads his main opponent, Prime Minister Raila Odinga, 53 to 42 percent.

However, Odinga's campaign manager maintains the prime minister will catch up once more votes from Odinga strongholds are counted.

Some Kenyans used social media Tuesday to vent frustration with the slow pace of the vote counting, and over an increasing number of rejected ballots.

Kenya's election commission says more than 300,000 ballots have been rejected so far. The commission chairman, Ahmed Isaack Hassan, suggested those ballots were marked incorrectly or dropped into the wrong box at pollling stations.

Kenyans Vote in Gatundu

Hassan appealed for patience and calm while the vote counting continues.

About 14 million Kenyans were eligible to vote in the elections for president, parliament, and other key offices. Both Odinga and Kenyatta have promised to respect the result of the vote.

Kenyatta faces trial at the International Criminal Court on charges he helped organize the ethnic violence which followed the disputed 2007 presidential election voting. More than 1,100 people were killed in that violence.

Monday's election in Kenya was mostly peaceful, although just hours before voting began, at least 13 people, including seven police officers, were killed along Kenya’s coast. Three suspects were arraigned in court Tuesday.

Kenya Map

Election chairman Hassan, who said there were no reported incidents of violence during voting hours, also added that voter turnout appears to have been above 70 percent.

Monday's voting took place under tight security, with nearly 100,000 police officers deployed across the country.

The U.S. State Department condemned what it called "isolated incidences of violence" in Kenya but said election observers reported the vote was generally calm and peaceful.